Oxygen free radicals are being implicated more and more as etiological agents in the development of several disease states including carcinogenesis and tumor promotion. Mechanistically, the exact role of oxygen free radicals in these processes is unknown. Competent and accurate assessment of in vivo levels of oxygen free radicals has held up progress. We made a novel observation, namely that using HPLC-electrochemical detection (LCED) it is now possible to detect subpicomole levels of an OH-adduct of a DNA nucleoside. The OH-adduct of deoxygtuanosine, 8-OHdG, is formed in DNA under conditions known to produce OH. We have found, for the first time in a biological system, that 8-OHdG is present in the DNA of human granulocytes stimuated to produce oxygen free radicals by exposure to the tumor promoter, TPA. Formation of 8-OHdG in the DNA was mediated by oxygen free radicals as evidenced by the decreased levels formed in cells treated with superoxide dismutase and catalase. Now that it is possible to detect 8-OHdG in the DNA of milligram amounts of tissue and thus perhaps begin to address questions relevant to the role of oxygen free radicals in the development of disease states, we consider it necessary to examine in depth the role of OH and Fe in the formation of 8-OHdG in three systems, namely dG in solution, DNA per se, and in the DNA of biological models. We have designed experiments to examine these systems in depth. The proposed bological models include human granulocytes exposed to TPA and Chinese Hamster Lung Fibroblasts (V-79) cells exposed to ionizing irradiation. In addition to examining 8-OHdG formation, we propose to determine if OH reacts with guanosine to produce 8-OHG which then can be detected by the LCED technique. This question will be addressed using guanosine, RNA per se, as well as in biological models. Our proposed studies may be very helpful to the design of future experiments examining mechanistically the role of oxygen free radicals in the development of disease states.